The present invention relates generally to bioadhesive polymer systems. In particular, the invention relates to the use of hyaluronic acid polymers for mucosal delivery of vaccine antigens and adjuvants.
Mucosal immunity provides an important defense mechanism against a wide variety of pathogens. In this regard, the mucosal surfaces of the gastrointestinal, respiratory and genitourinary tracts are continuously exposed to foreign antigens, including potentially infectious bacterial, vial and sometimes parasitic organisms. Mucosal immune responses protect against such challenges and have distinct and specialized characteristics.
For example, the principal immunoglobulin produced by the mucosal immune system is secretory IgA. Specialized antigen uptake cells in the Peyer""s Patches of intestinal tract or nasopharyngeal lymphoid tissues, termed microfold or M cells, transport antigen to the underlying mucosal associated lymphoid tissues (MALT). In other areas of the mucosal epithelium, such as the pseudo-stratified airway epithelium, dendritic cells serve as antigen-presenting cells and migrate to local lymph nodes or MALT. Antigen processing and presentation occurs in the MALT, resulting in activation of antigen-specific IgA B cells. The subsequent trafficking and recirculation of the activated IgA-B cells to other components of the mucosal immune system, e.g., the respiratory, intestinal and genital tracts, provides for disseminated local mucosal IgA responses throughout the xe2x80x9cCommon Mucosal System.xe2x80x9d Thus, the mucosal immune system is uniquely suited to respond to the types of antigenic challenge encountered by mucosal surfaces and may provide the most effective type of immune response against particular pathogens. Accordingly, antigen delivery mechanisms which target the mucosal immune system provide an attractive means for achieving immunity.
Attempts have been made to use bioadhesive polymers for the mucosal delivery of drugs. Bioadhesives are synthetic and naturally occurring materials able to adhere to biological substrates for extended time periods. For example, Carbopol and polycarbophil, both synthetic cross-linked derivatives of poly(acrylic acid), display excellent adhesion properties in vitro. However, performance of these bioadhesives has not been duplicated in vivo. Additionally, such bioadhesives may cause local irritation. Hence, few bioadhesive delivery systems are commercially available.
Attention has therefore turned to the development of bioadhesive delivery systems based on naturally occurring substances, such as lectins and fimbrial proteins. These bioadhesives adhere to mucosal cell surfaces via receptor-mediated mechanisms. Another natural bioadhesive is hyaluronic acid, also known as hyaluronan. Hyaluronic acid is a naturally occurring mucopolysaccharide consisting of residues of D-glucuronic and N-acetyl-D-glucosamine. Hyaluronic acid is found in the extracellular tissue matrix of vertebrates, including in connective tissues, as well as in synovial fluid and in the vitreous and aqueous humour of the eye. Hyaluronic acid has been shown to be bioadhesive both in vivo and in vitro.
Esterified derivatives of hyaluronic acid have been used to produce microspheres that are biocompatible and biodegradable. See, e.g., Cortivo et al., Biomaterials (1991) 12:727-730; European Publication No. 517,565. These microspheres have been used for the mucosal delivery of a number of substances. See, e.g., International Publication No. WO 96/29998. For example, Richardson et al., Int. J. Pharm. (1995) 115:9-15), describe the vaginal delivery of calcitonin in rats. Additionally, Illum et al., J. Controlled Rel. (1994) 22:133-141 and European Publication No. 517,565 describe the use of hyaluronic acid ester microspheres for the intranasal delivery of insulin in sheep.
However, the use of hyaluronic acid derivatives to deliver vaccine antigens has not heretofore been described.
The present invention provides an effective method for eliciting an immune response in a mammalian subject using mucosal immunization and hyaluronic acid delivery techniques. The present invention is based on the discovery that the mucosal delivery of hyaluronic acid derivatives, such as esterified hyaluronic acid polymers and auto-crosslinked hyaluronic acid polymers, in combination with an antigen of interest, and optionally an adjuvant, acts to enhance the immunogenicity of the antigen coadministered therewith. While not wishing to be bound by a particular theory, it is believed that the bioadhesive properties of the hyaluronic acid polymers decrease the rate of mucociliary clearance from the nasal cavity and thus allow a longer contact time between the antigen and the absorbing membrane. Additionally, a transient widening occurs at the tight junctions between the cells of the mucosal epithelia allowing more efficient transport of the antigen of interest. The use of hyaluronic acid polymers provides a safe and effective approach for enhancing the immunogenicity of a wide variety of antigens.
Accordingly, in one embodiment, the invention is directed to a composition comprising an hyaluronic acid ester polymer and a selected antigen, wherein the antigen is present in an amount of approximately 0.1% to about 40% (w/w) antigen to hyaluronic acid polymer.
In particularly preferred embodiments, the hyaluronic acid ester is selected from the group consisting of an hyaluronic acid where from about 75% to about 100% of free carboxyl groups are esterified with one or more alkyl groups, and a crosslinked derivative of hyaluronic acid in which about 0.5% to about 20% of the carboxyl groups of the hyaluronic acid polymer are crosslinked to hydroxyl groups of the same or a different hyaluronic acid molecule.
In another embodiment, the invention is directed to a composition comprising (a) a microsphere comprised of an hyaluronic acid ester selected from the group consisting of an hyaluronic acid where from about 75% to about 100% of free carboxyl groups are esterified with one or more alkyl groups, and a crosslinked derivative of hyaluronic acid comprising internal esters in which about 0.5% to about 20% of the carboxyl groups of the hyaluronic acid polymer are crosslinked to hydroxyl groups of the same or a different hyaluronic acid molecule; (b) a selected antigen entrapped in, or adsorbed to, the microsphere, wherein the antigen is present in an amount of approximately 2% to about 25% (w/w) antigen to hyaluronic acid polymer, and (c) an immunological adjuvant.
In still further embodiments, the subject invention is directed to methods of making pharmaceutical compositions which comprise combining the compositions above with pharmaceutically acceptable mucosal excipients, as well as methods of immunization comprising mucosally administering therapeutically effective amounts of the pharmaceutical compositions to a vertebrate subject.
These and other embodiments of the present invention will readily occur to those of ordinary skill in the art in view of the disclosure herein.